1. Field of the Invention
This invention relates to the field of light filtering and filtering devices. Specifically, the invention relates to a portable light filtering device that uses multiple sheets of polarized film.
2. Background
Reducing transmitted light is useful for vehicles, buildings, homes and anywhere else that it may be desired to reduce the amount of light entering a space. Reducing the light passing through glass has been solved in several different ways.
Tinted film can be attached directly to the inside of glass. This tends to be permanent and may be too dark which can compromise night vision and if used on vehicle glass in some states, it can result in a police citation.
Shades or blinds are practical in homes and buildings but are not very practical in vehicles.
Plasma addressed liquid crystal (“PALC”) can be used to assume an opaque state to reduce the transmission of light through glass. For example, see U.S. Pat. Nos. 6,674,419 and 7,245,205. However, the use of PALC requires sophisticated electronic controls and the PALC material alone is exceedingly expensive.
Window tinting using polarized film is known. Polarized film has been used in a single layer and in multiple layers to block light or vary the amount of light that is transmitted through glass.
When polarized film is used, either in a single layer or in multiple layers; it is incorporated into a complex assembly that becomes an integral part of the window unit. For example, in U.S. Pat. No. 5,940,216 two layers of polarized film are used, with the lines of polarization of each layer being parallel to the other layer. The lines of polarization are shifted relative to the other layer by using a relatively complex motor and cam mechanism.